Debarking equipment for removing bark from logs prior to additional processing by other wood processing equipment is well known. Examples of prior art debarking equipment known to the inventors includes the following patents:
U.S. Pat. No. 3,190,327 to Robbins
U.S. Pat. No. 3,862,653 to Fay et al.
U.S. Pat. No. 3,863,692 to Hasada et al.
U.S. Pat. No. 4,691,750 to Nakajima
U.S. Pat. No. 4,771,953 to Morey
U.S. Pat. No. 5,070,919 to Ackerman; and
U.S. Pat. No. 5,117,881 to Simpson
Many existing designs for debarking equipment rely on a drum arrangement into which logs to be debarked are fed. The drum is mounted for rotation about a generally horizontal, longitudinal axis and the inner surface of the drum has a sequence of longitudinal flights or ridges that run parallel to the axis of rotation. As the drum is rotated, the flights act to carry the logs to an elevated position where they are dropped due to gravity to make contact with other logs and lower flights which act to remove bark from the logs by abrasion.
The rate at which logs are debarked in a drum-type debarker depends on various factors including log condition, log diameter, temperature, and log species which all affect the adherence of the bark to the underlying wood.
Conventional drum-type debarking equipment suffers from the disadvantage that it is limited in its ability to control and vary the rate of debarking. When conditions are such that bark is easily removed from a batch of logs, the residence time of the logs in the drum until the bark is removed is reduced. If a batch of logs has bark that is more difficult to remove, the residence time has to be increased. In some equipment, the drum can be rotated at different speeds. A slower rotation speed accommodates logs with easily removed bark while a faster speed tends to debark more difficult logs with approximately the same residence time.